exponents

[cool dude]

how would you make an exponent with BigInteger.

i want to get the answer of 2 ^1000 so i need to know how to make this using BigInteger.

[rizzix]

Java:

BigInteger result = new BigInteger(2).pow(new BigInteger(1000));

[wtd]

I can't help myself. Post #4500 is:

code:

(expt 2 1000)

[rizzix]

Haskell:

2 ^ 1000

or

Haskell:

(^) 2 1000

However you like it.

[cool dude]

rizzix wrote:

Java:

BigInteger result = new BigInteger(2).pow(new BigInteger(1000));

it says cannot resolve symbol constructor BigInteger(int)

Can someone please make a tutorial on BigInteger! i would be really grateful. as you can tell from all my posts i am not understanding how to use BigInteger. would you rather me post 100 posts about BigInteger

[McKenzie]

Two problems.
1. You can't make a BigInteger with an int, use "2" (seems foolish, I agree)
2. The pow does take an int not a BigInteger (you would think it would be overloaded)

[Martin]

cool dude wrote:

rizzix wrote:

Java:

BigInteger result = new BigInteger(2).pow(new BigInteger(1000));

it says cannot resolve symbol constructor BigInteger(int)

Can someone please make a tutorial on BigInteger! i would be really grateful. as you can tell from all my posts i am not understanding how to use BigInteger. would you rather me post 100 posts about BigInteger

Well, here's one way you could do it:

Java:

BigInteger result = new BigInteger("2").pow(1000);

The best way to learn how to use it is just to read the API docs (click on the keywords in the syntax highlighted java code).

[rizzix]

Sorry, my mistake. Yes you have to use a string and pow only accepts ints (primitives).

You don't need a tutorial on BigInteger. The problem here is that you're confusing the BigInteger object with a java primitive. There is a distinction between the two. Objects behave differently and primitives behave differently. If you keep that in mind, you'll make less mistakes.

Secondly, you must take a good look at the method signarurs in the Java API docs. Make sure you are passing the right "typed" argumets to the respective methods. That's all.

[cool dude]

k thanks. also how would i convert BigInteger to String? i tried this:

code:

String sresult = BigInteger.toString(result);

and how would i get the length of the BigInteger?

[cool dude]

k i figured out how to convert it to string and how to get the length of that string. the only problem now is when i try and run my program it says:

Quote:

Exception in thread "main" java.lang.NumberFormatException: For input string: ""

...

this is my code:

code:

import java.math.*; public class Problem16{         public static void main (String[] args){                 int sum = 0;                 BigInteger result = new BigInteger("2").pow(1000);                 String sresult = result.toString();                 int n = sresult.length();                 for (int i = 1; i < n; i ++){                         sum = sum + Integer.parseInt((sresult.substring(i,1)));                 }                 System.out.println (sum);         } }

[wtd]

Check out the documentation for the substring method in the String class, and the static parseInt method in the Integer class.

[cool dude]

i changed my code a little around and tried different variations but its still the same error! i did read the documentation for the substring method and i know how it works. i also know from other languages and its pretty much the same. i'm not sure where my problem is though. you keep telling me to read the documentations and i do read them but i can not pinpoint the problem.

Here's my newer code which still doesn't work

code:

import java.math.*; public class Problem16{         public static void main (String[] args){                 int sum = 0;                 BigInteger result = new BigInteger("2").pow(1000);                 String sresult = result.toString();                                 for (int i = 0; i < sresult.length(); i ++){                         sum = sum + Integer.parseInt(sresult.substring(i,1));                 }                 System.out.println (sum);         } }

[wtd]

I suggested investigating two methods.

Do you know how Integer's static parseInt method works?

[r.3volved]

First thing I noticed is your for loop. Not much of a problem, but the correct syntax would be:
for(int i = 0; i != sresult.length(); ++i)

it seems to choke when the substring hits a 0 (ZERO)

code:

import java.math.*; public class Problem16 {     public static void main (String[] args)    {       int sum = 0;       BigInteger result = new BigInteger("2").pow(1000);       String sresult = result.toString();             for (int i = 0; i != sresult.length(); ++i)       {         sum += Integer.parseInt(sresult.substring(i,i+1));       }       System.out.println(sum);    } }

Try that...debugging the code killed my netbeans
but I also noticed your substring was incorrect

[cool dude]

thanks for the help. 2 questions

1) what is the difference between your counted loop and mine? they perform the same thing.

2) i'm now totally confused on the substring because i thought the second digit meant how many letters to take, thus i always put 1. but why i + 1? so if i = 5 then you would take 6 numbers? i only want one number not 6. i don't get how that works